Controlling nitrogen oxide (“NOx”) emissions in diesel engines has posed significant challenges to the automotive industry. Several different methods of controlling NOx emissions from diesel engines have been proposed. One type of method is generally known as low-temperature diesel combustion. This method utilizes an early or late injection of fuel into the combustion chamber of the engine so that the fuel burns at lower temperatures. The lower combustion temperatures produce lower concentrations of NOx byproducts.
Both the early and late injections of fuel allow the fuel to mix more thoroughly with air than ordinary diesel combustion, and are therefore sometimes referred to as “early homogenization combustion” and “late homogenization combustion,” respectively. Likewise, ordinary diesel combustion may be referred to as “diffusion” combustion due to the fact that combustion occurs with comparatively less mixing of fuel and air in the cylinder.
While low temperature combustion is effective to reduce NOx emissions to a substantial degree, these techniques may still fail to remove sufficient NOx for a diesel engine to meet modern emissions standards. The inventors herein have recognized that the reduction of NOx emissions from a diesel engine may be more efficiently addressed by utilizing a method of operating a diesel engine that utilizes a catalyst configured to treat NOx emissions from the engine, wherein the method includes performing at least one early homogenization combustion in the combustion chamber, determining a temperature of the catalyst, and if the temperature of the catalyst is equal to or below a preselected temperature threshold, then performing at least one late homogenization combustion or diffusion combustion in the combustion chamber to raise a temperature of exhaust provided to the catalyst.